The application of lighting to the automotive industry is well known. The original electric light sources were filament bulbs which offered high luminance from a small source. Improvements in light source design led to halogen type filament bulbs, high intensity discharge (HID) bulbs or high brightness light emitting diodes (LED). These offer improvement in terms of luminance and energy use over preceding filament bulbs. In order to apply these light sources to automotive front lighting and realise the beam spot distributions required by regulatory bodies, such as the United Nations Economic Commission for Europe (UNECE) or Federal Motor Vehicle Safety Standards (FMVSS), for the U.S.A, modification of the output beam to form specific beam spot distributions on the road is necessary. For projector headlights this requires removal of a portion of the light from the projected beam which ultimately forms the beam spot, to create a dipped beam. The dipped beam is necessary to avoid causing glare to oncoming road users. By necessity, the dipped beam also creates a restricted view of the road due to restricted illumination of the same. The removal of light is performed by a shield, which is inserted into the light path thereby causing a reduction in optical efficiency of the projector headlight.
The filament and discharge light sources provide no means for modification of the output from the source. Therefore, a shield is the only method of providing the dipped beam spot distribution pattern. To switch between a dipped beam and a driving beam, the beam pattern that is necessary for better visibility, either two headlights must be provided, one to create the dipped beam and the other to create the driving beam, or a mechanical switching mechanism must be provided. When the driving beam is desired, the mechanical switching mechanism removes the shield from the projected beam profile allowing all light to exit the projector headlight unit unimpeded.
The provision of only a dipped beam distribution, or of only a driving beam distribution, has limitations in terms of road user safety by not providing simultaneous optimal illumination of the road and minimal glare to other road users. This can be improved upon by the addition of an adaptive element to the projected headlight beam. However, all methods of creating an adaptive beam spot from a single projector unit require mechanical moving components within the headlight unit. This has a limitation on cost reduction and reliability of the headlight over the course of its lifetime. Alternative methods of provision of an adaptive beam spot require multiple light source units, which increases the headlight cost, and which also have a large volume, this having implications for pedestrian safety in the event of a collision.
Laser based light sources offer advantage over existing light sources due to the ability to control the emission from the laser diode effectively using optics with a much reduced size, and therefore, weight. This control ability stems from the small emission area and restricted angular distribution of the laser diode. The light emitted from laser diodes is often illuminated onto a fluorescent material to convert from the first wavelength to a second wavelength, which is predominantly white. The light source created is very small and can be used more efficiently with headlight projection optics.
The following background art describes the use of lasers in automotive headlight units:
U.S. Pat. No. 7,654,712 B2 (Koito Manufacturing, 28 Jun. 2006); an illustration of this patent is shown in FIG. 1. A lamp for a vehicle 11 is disclosed as comprising an optical member 12 which distributes the light emitted from the light source 13. The light source is disclosed as comprising a surface emitting laser element 14 which excites a fluorescent substance 15. The surface emitting laser element 14 may be controlled as a function of position to give an adaptively controllable light source 13 with reduced size. The surface emitting laser element 14 is illustrated as being integrated with the fluorescent substance 15, this is shown in FIG. 2 and therefore illuminating the fluorescent substance 15 on a side opposite 16 to the optical member.
US 2012-0051074 A1 (Sharp, 31 Aug. 2010); an illustration of relevant aspect of this patent is shown in FIG. 3. A lighting apparatus 35 is disclosed. The lighting apparatus 35 is formed from a fluorescent member 31 which is illuminated by laser light 32 from the front side 33. The front side is shown as being the same side as the projecting lens 24. The lighting apparatus 35 may be adaptive in beam control through scanning of the laser light 32 across the fluorescent member 31. The illumination spot may have varying position and/or area.
JP 2010-232044 A (Stanley Electric Co, 27 Mar. 2009); an illustration of this patent is shown in FIGS. 4 and 5. The patent discloses a lamp 41 for a vehicle. The lamp 41 is comprised of an array of LED emitters 42 and a fluorescent substance 43. The fluorescent substance 43 is illuminated by a laser emitter 51 (FIG. 5) which is concentrated upon the fluorescent substance 43 by a collimating lens 52. The laser emitter 51 is disposed on the same side of the fluorescent substance 43 as the convex lens 44.
JP 2011-134619 A (Stanley Electric Co, 25 Dec. 2009); an illustration of this patent is shown in FIG. 6. This patent discloses light source device 61 which comprises a solid state light source 62 which illuminates a fluorescent material 63. The light emission 64 from the fluorescent material 63 is projected into the far field by a lens system 65. The light from the solid state light source 62 may be controlled by an articulated reflector 66. The fluorescent material 63 is illuminated from the same side as the lens system 65.
FIG. 7 is an illustration of the basic form of a typical projector type light source system 74. A source of light 71 is located at the primary focal point 72 of an ellipsoidal reflector 73. The light emission 75 from the source of light 71 is directed to the secondary focal point 76 of the ellipsoidal reflector 73. A projection lens 714 images the distribution of brightness at the secondary focal point 76 into the far-field, to form a beam spot. Adaptive control of such a projector type light source system 74 requires mechanical control comprising either re-orientation of the entire system, or complex mechanisms which modify the distribution of brightness at the second focal point 72. The complex mechanisms are well known and will not be described further.
US 2011/0249460 (T. Kushimoto, 13 Oct. 2011), proposes a vehicle headlight having an array of phosphor squares, which are illuminated by light from blue laser sources. Light from a laser source is directed onto the back surface of the phosphor grid by a mirror.